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Doctors perform sleep studies or polysomnography (PSG) to diagnose sleep related illness or symptoms. Traditionally, patients have a diagnostic study performed for an entire night to diagnose obstructive sleep apnea (OSA). Once the doctor confirms OSA, he sets up a separate therapeutic study. During this second study the doctor adjusts (or titrates) continuous or bilevel positive airway pressure (CPAP or BiPAP) to levels that eliminate or significantly reduce the number of respiratory abnormalities (apneas and hypopneas).

Doctors perform therapeutic PSG with CPAP titration if patients have a diagnostic study demonstrating an apnea-hypopnea index (AHI). They may also perform it if the patient's respiratory disturbance index (RDI) of at least 20 events per hour regardless of symptoms or an AHI/RDI of 10 events per hour associated with excessive daytime somnolence (EDS).

To reduce costs and improve efficiency many centers now combine the diagnostic and therapeutic studies into a single night, called a split-night study. Research by Yamashiro and Kryger, as well as Rodway and Sanders have demonstrated the effectiveness of this strategy especially in patients with significant elevations in AHI/RDI. Split night studies are now incorporated into the guidelines for treatment of OSA published by the American College of Chest Physicians (ACCP).

Split-night polysomnography (PSG) divides the patients testing into two phases in one night. During the first part of the night, sleep specialists diagnose obstructive sleep apnea (OSA) and the second half determine the appropriate level of positive airway pressure (CPAP or BiPAP). Medical necessity guidelines for PSG must meet two conditions for healthcare plan payments. The patient must show a respiratory disturbance index (RDI) greater than 40 during the first two hours of testing; or a RDI of 20-40 if associated with prolonged events or significant desaturations. Split night testing has shown to be less dependable in patients with AHI/RDI measurements less than 20 events per hour. Some doctors have been successful utilizing a split night strategy in patients with AHI/RDI as low as 10 events per hour if associated with EDS, impaired cognition, mood disorders, or documented hypertension, heart disease, or a history of stroke.

There is good evidence that split-night studies can be used under these guidelines. The challenge is that the patient must fall asleep promptly and demonstrate an elevated RDI early in the evening. Only about 25-30 percent of patients have successful split-night studies. The patient must have at least two hours of sleep documented in the diagnostic phase of the study with the documented increase in AHI/RDI. At least three hours of time is necessary for the therapeutic phase.

If the RDI is elevated early in the sleep cycle, then the patient is awakened. The specialist places a pre-fitted CPAP mask on the patient and then patient resumes sleep for another three hours as the pressure is titrated to eliminate the respiratory events. That is, the first part of the split study is diagnostic, and the second is therapeutic.

When a split-night study cannot be accomplished, then a therapeutic titration study is indicated. There is no specific timeframe for the performance of a titration (therapeutic) study after a diagnostic study. It should be done as soon as is practical.

Requesting a split-night study is a very cost effective strategy. If 100 percent of the studies in a practice or sleep lab were done by means of separate diagnostic and therapeutic studies on two separate nights this would indicate that the recent recommendations regarding the effectiveness of split night studies were overlooked. Seventy to 75 percent of studies may require two separate nights.

Include a specific statement about why a split night study could not be accomplished helps in the patient's file to indicate the necessity for a second study.